Plant metabolism has evolved the ability to produce a diverse range of structures, including more than 20,000 different terpenoids, flavonoids, alkaloids, and fatty acids. Fatty acids have been extensively exploited for industrial uses in products such as lubricants, plasticizers, and surfactants. In fact, approximately one-third of vegetable oils produced in the world are already used for non-food purposes (Ohlrogge, J (1994) Plant Physiol. 104:821-26).
In 1999, approximately 40 million hectares of transgenic crops were planted worldwide. Included in this figure is approximately 50% of the soybean acreage in the United States, over 70% of the Canola acreage in Canada, about 20% of the United States corn crop, and about 33% of the United States cotton crop (Ohlrogge, J (1999) Curr. Opin. Plant Biol. 2:121-22).
Various laboratories around the world have attempted to modify triacylglycerol (TAG) content in oilseed crops by manipulating the genes involved in TAG biosynthesis. The TAG biosynthetic pathway involves many enzymatic reactions. An increasing number of the genes that encode these enzymes have been cloned and studied in detail with respect to the quantitative and qualitative contributions they make to the TAG composition of a particular oilseed. There are still several genes in the TAG pathway, however, that have not been cloned and characterized in detail.
Most of the efforts to modify TAG content have focused on either increasing the nutritional characteristics and chemical stability of edible oils or on introducing new and unusual fatty acids into TAGs for use in various industrial applications. Progress has been achieved through over-expression and/or suppression of a modestly small number of genes in the TAG synthesis pathway. However, to date, the alterations in fatty acid content have not been substantial enough to create truly meaningful new oilseed lines.
Thus, there remains a need to identify and characterize additional genes in the TAG synthesis pathway, the manipulation of which can contribute to altered or increased fatty acid content in oilseeds.